Sometimes storing electricity makes no (energetic) sense

For wind, discarding the energy may be more efficient than building big batteries.

Two of the major renewable energy sources, wind and solar power, are intermittent in that they can't always be relied on for power. Although there are many strategies for mitigating the impact of the interruptions, the intermittency is thought to place a limit on the percentage of renewable power that can be easily integrated into the electric grid (although the precise point at which it becomes a problem is a bit of a moving target).

One approach to intermittency is to store electricity from these sources for use when they're not active. GE even offers an integrated wind energy/battery system that's meant to do precisely that. But a new analysis by Stanford researchers suggests that this approach might be misguided. Wind turbines are so cheap to build energy-wise, compared to batteries, that it's better just to discard the energy. By contrast, solar power pairs well with batteries in this analysis.

The problem with intermittency is matching supply with demand. The authors of the study cite data from Texas, which has seen a boom in wind generating capacity but hasn't built transmission lines fast enough to get the energy where it's needed. As a result, 13 TeraWatt hours of electrical energy have been discarded over the last five years. In some years, as much as 17 percent of the wind energy produced in Texas went unused.

There are a variety of means of storing electricity for future use, however. Some require large facilities like pumped hydro power or compressed air storage. Others, like batteries, can be distributed. But producing the storage capacity also takes money and energy, which cuts into the production from renewable power. The new study takes a look at this balance from the perspective of a value called energy return on investment (EROI).

The basics of EROI are pretty simple: it costs energy to produce energy, whether the cost is involved in mining coal or purifying silicon to produce a photovoltaic power. To be effective, the energy you get access to as a result will have to be higher than your initial investment. For renewable energy sources, this varies a great deal based on the precise technology used (thin film vs. silicon solar panels) and how that technology is put to use. For example, depending on the precise location of a wind turbine, the break even point for energy may be as little as months or as much as a few years, resulting in very different EROI values.

The same thing is also true for energy storage. Dams, generators, and pumps are all required for pumped hydro storage, all of which take energy to make. The same applies to batteries. The authors generated an equivalent of EROI for storage technologies, taking into account the amount of energy that can be stored, the efficiency with which it can be retrieved, and so on.

The good news is that both pumped hydro and compressed air storage provide excellent returns on the energy invested and can be successfully paired with both wind and solar power. The bad news is that even the best lithium batteries are almost two orders of magnitude worse, and things like lead-acid batteries come up short by yet another order of magnitude. This changes the results for the different sources of renewable energy significantly. Solar panels take a lot more energy to produce, so preventing the waste of that invested energy pays off, even if it's done with a low-energy payback using batteries.

By contrast, the authors conclude, "Attempting to salvage energetically cheap power (e.g., wind) using energetically expensive batteries is wasteful from a societal perspective." Elsewhere, they note, "if society aims to increase output of (say) wind energy with the least energetic investment, it is better in many cases to just build another wind turbine, or possibly transmission lines, than to build a battery to store power that arrives at off-peak times."

After looking over why their model gave this output, the authors conclude that the simplest way to change the situation is to give batteries a longer usable lifetime. Simply doubling the usable life of a lithium battery would be enough to start shifting battery storage of wind power into the break-even territory (increasing capacity and the ability to sustain larger drains would also help).

By the authors' own admission, their model doesn't account for everything. For example, they note that distributed storage can improve the stability of the electric grid and provide backup power to key facilities in emergencies, things that produce non-energetic value. The geological features that enable pumped hydro and compressed air aren't available in all locations either, which means that it may be a choice of battery storage or none at all. The authors' estimates can also be thrown off if the amount of storage capacity built is a poor match for the typical excess of electricity.

The last thing they suggest, however, is that having excess electricity may be a net societal benefit, allowing us to do things like desalinate water or produce materials that would otherwise be energetically prohibitive.

172 Reader Comments

One of the more efficient energy storage tactics is to use the excess power from an unpredictable source to pump water uphill into a tank/reservoir and store it as potential energy. When the energy is needed, let the water flow downhill through a turbine. The good thing is that once the water is up there, it stays up there (with the exception of relatively small losses from evaporation, of course). A battery can't hold a charge indefinitely, but the water will stay at the top of the system until it's unleashed.

Pumped-hydro was already discussed in the story, and it's certainly not one of the most efficient methods... A little thing like evaporation may sap 30% of your power storage with normal cycles, and long-term storage you can definitely come out with 0 return. Meanwhile, at least low-self discharge NiMH batteries lose only about 15% of their charge per YEAR, so for long-term storage, batteries are clearly better, though of course there are still-better options out there.

Try 5-10% per year for low self discharge cells, eneloop makes NiMH cells that retain 90% after 1 year and 80% after 3 years. I'm not sure their tech scales up to grid scale and it almost certainly makes no sense to store grid scale amounts of energy for years at a high cost premium, much better to have a battery that leaks 10% per day but costs 90% less per KWhr which is why pumped water and thermal batteries work out.

Storing 13TWh of electricity in batteries in current is actually impossible, there is not even enough lead in the world. Even storing that much energy in Li-batteries is only marginally possible on a theoretical scale.

What people simply do not grasp is that fossil fuels are just about the physically optimum form to store energy per mass via the electromagnetic force. Only Hydrogen is better, but it does not exist freely in nature. This is a hard physical limit and there will not be anything better than our hydrocarbon fuels for the electromagnetic force.

In terms of battery technology we have also exhausted our possibilities. It cannot get better than Li-based batteries. That's it. There is no lighter metal left. There is no lighter charge carrier than a proton left. So, better start getting used to the current capabilities of batteries, physics guarantees that there is no game changer left in the game. Only minor refinements are possible from now on.

Oh, and did I say that batteries are horrendously expensive? They cost 1-2$ per kWh delivered. Compare this with 0.03c/kWh for electricity via natural gas power plants.

i know the concept, i was questioning the scale - would it actually be a problem to lift a solid object instead of pumping water?

'cause i imagine it would be more efficient

obviously there's some problem or they would be doing it, but i'm interested in what the problem is

The trick with water is that (as you probably realise) it can be lifted bit by bit while an equivalent object of the same mass needs to be lifted in its entirety. So while it's a trivial problem to pump 10 tons of water through pipes 400 foot, moving 10 tons of steel is not a trivial problem as crane, lorry, and lift manufacturers will confirm. Moving 10,000 tons of water quickly starts to get into the non-trivial problem category while 10,000 tons of steel (in a way that's as useful for this purpose as water) is un-feasible.

i know the concept, i was questioning the scale - would it actually be a problem to lift a solid object instead of pumping water?

'cause i imagine it would be more efficient

obviously there's some problem or they would be doing it, but i'm interested in what the problem is

The trick with water is that (as you probably realise) it can be lifted bit by bit while an equivalent object of the same mass needs to be lifted in its entirety. So while it's a trivial problem to pump 10 tons of water through pipes 400 foot, moving 10 tons of steel is not a trivial problem as crane, lorry, and lift manufacturers will confirm. Moving 10,000 tons of water quickly starts to get into the non-trivial problem category while 10,000 tons of steel (in a way that's as useful for this purpose as water) is un-feasible.

ok, that makes sense - still, you could simply divide that huge solid object into n smaller objects, tho' that would introduce the problem of switching to the next one whenever one is lifted/lowered all the way

also, lifting 10 tons is a very trivial problem judging by a quick glance at some cranes http://www.bigge.com/crane-charts/ (some of those list over a kiloton)and obviously for our purposes, it wouldn't have to be mobile and would likely only need to work vertically, so that would make it even easier

Why not use the unneeded power for other useful energy expensive activities? I saw something a while back about small scale water desalination facilities.. maybe set some of those up near the windfarms and purify water in the off hours. Last I heard Texas has a shortage of fresh water.. this could be a win/win for them..

So...your plan is to have a desalinization plant idle just waiting for when then wind picks up and there happens to be too much energy?

In the Netherlands we have a windpark at 15km off the coast (Egmond aan Zee) generating 108 MW, so - sure, why not?

Lithium batteries are finicky and need careful handling and proper charging. Maybe these don't work well in the cold, or maybe in the heat, can't tell from the information at hand. From the Tesla journalist drive, it seems cold does bad things to the Tesla lithium battery capacity.

For the other readers here: none of this is correct.

*Some* lithium designs, specifically lithium cobalt, have charging safety issues. Other designs, like lithium iron (in the Tesla and other e-cars) do not suffer from these issues, at the cost of somewhat reduced capacity. Why Boeing chose to go with LiCo on the Dreamliner is a complete mystery to me, something anyone in the industry would have warned against.

In terms of cold, modern LiFePO batteries lose about 15% of their capacity at zero Celsius compared to the same battery at 25 Celsius (STP). For comparison, lead-acid loses about 30 to 40% of its capacity over the same temperature range, while gel cells are somewhat better. For grid storage, heating the batteries, any type, is a very realistic scenario, as they can be built into highly insulated buildings and self-heat in use.

I've read [insert random Wikipedia article here]. That makes me [an expert/wise to the conspiracy/able to see things others can't] and I've spotted [the flaw in the argument/perfect solution/way to stop The Man]. We should [insert semi-plausible sounding technological solution/destroy all the energy companies/run the test at home to check]. Blame [Obama/George Bush/John Ringo].

Actually, thermal storage is one of the common use cases for load shifting, many office buildings freeze water during the night when electricity is cheap and use it to cool the air during the day. To a lesser extent an intelligent grid could see the overproduction from wind coming and check to see if future temperatures looked to be cold or hot enough and adjust thermostats up or down a few degrees to shift consumption by a few hours (ie pre-cool or pre-heat buildings to use peak production to offset future demand). This kind of short term useful load storage is probably much more EROI efficient than any form of dedicated storage since it doesn't require the manufacturing of any storage mechanism, just the temporary shifting of loads.

Another form that will hopefully develop over the next few years is EV charging. My Leaf is plugged in from the moment I get home and until I leave, but for now it just uses a "dumb" timer to decide when to actually charge (scheduled for lower night time rates). The car already has a built in cellular data connection, it would just need a software upgrade in order to charge based on grid load data instead. Using EVs to make up for a shortage on the grid, or for power conditioning might also be practical, although a bit more complicated.

Actually, I seem to recall reading an article about that very concept. I don't recall where it was, but I want to say it was Ars. A quick search didn't turn it up, but that idea does not feel like a new one to me. And I'm not creative enough to have come up with it on my own.

It's no secret that batteries aren't the best way to store energy.. but why does that make storing excess energy nonsensical? Were any other methods of energy storage tried besides batteries? Sure, cost and lack of appropriate technology may synergize to make storing the excess energy undesirable logistically and budget wise, but it will never make energetic sense to discard energy. Ever.

I've always thought that hydrogen production is a great solution to our problems with excess energy from renewable sources, as well as bridging the gap between when the environment (sun and wind) is cooperating and when it is not. Use the excess energy to power hydrogen processing, store the hydrogen, and burn it to run traditional power generation methods until the resources are available again.

All I keep hearing is how the current solutions we have won't work.. folks, hate to break it to you, but doing things differently than we have been for almost the past 100 years will take us doing things a little differently.

i know the concept, i was questioning the scale - would it actually be a problem to lift a solid object instead of pumping water?

'cause i imagine it would be more efficient

obviously there's some problem or they would be doing it, but i'm interested in what the problem is

The trick with water is that (as you probably realise) it can be lifted bit by bit while an equivalent object of the same mass needs to be lifted in its entirety. So while it's a trivial problem to pump 10 tons of water through pipes 400 foot, moving 10 tons of steel is not a trivial problem as crane, lorry, and lift manufacturers will confirm. Moving 10,000 tons of water quickly starts to get into the non-trivial problem category while 10,000 tons of steel (in a way that's as useful for this purpose as water) is un-feasible.

ok, that makes sense - still, you could simply divide that huge solid object into n smaller objects, tho' that would introduce the problem of switching to the next one whenever one is lifted/lowered all the way

also, lifting 10 tons is a very trivial problem judging by a quick glance at some cranes http://www.bigge.com/crane-charts/ (some of those list over a kiloton)and obviously for our purposes, it wouldn't have to be mobile and would likely only need to work vertically, so that would make it even easier

Its interesting how potential surplus energy is ahead of the means to transport it. Is there real interest put by those corporations into fixing it? The social perception "wasted energy" will demand it to be given for free to some communities or institutions.

Seems like the problem is not demand, but rather getting the energy to consumers. The article implies that it's a lack of transmission lines that leads to this energy dumping.

i know the concept, i was questioning the scale - would it actually be a problem to lift a solid object instead of pumping water?

'cause i imagine it would be more efficient

obviously there's some problem or they would be doing it, but i'm interested in what the problem is

The trick with water is that (as you probably realise) it can be lifted bit by bit while an equivalent object of the same mass needs to be lifted in its entirety. So while it's a trivial problem to pump 10 tons of water through pipes 400 foot, moving 10 tons of steel is not a trivial problem as crane, lorry, and lift manufacturers will confirm. Moving 10,000 tons of water quickly starts to get into the non-trivial problem category while 10,000 tons of steel (in a way that's as useful for this purpose as water) is un-feasible.

ok, that makes sense - still, you could simply divide that huge solid object into n smaller objects, tho' that would introduce the problem of switching to the next one whenever one is lifted/lowered all the way

also, lifting 10 tons is a very trivial problem judging by a quick glance at some cranes http://www.bigge.com/crane-charts/ (some of those list over a kiloton)and obviously for our purposes, it wouldn't have to be mobile and would likely only need to work vertically, so that would make it even easier

I keep kicking that idea around in my head too, but i think the problem is that a system that can store a useful amount of power would be massive. I was surprised by how little power it takes to lift a really heavy weight quite a long way.

Try going the other way, imagine the largest system that could be built then calculate the amount of energy that could be stored in that way. Is it physically practical to move aloft a 30mx30mx30m block of iron 300m? You could build the system into a used quarry or something so you wouldnt have to build a giant building to support it. I have to go to a meeting so i dont have time to run the numbers, but im guessing that the amount of power stored isnt really that much. Still you could store it essentially forever.

Why not split water into oxygen and hydrogen? You can store a lot, and burn it off in fuel cells or even piston-engined grid-tie generators. It's inefficient, but so's throwing out the energy entirely.

I'm not an expert in power generation and storage, but I think storing large volumes (incredibly massive volumes... the volume of gas produced from even a few ml of water is substantial) of explosive gases is NOT a good idea. The designers of the Hindenburg learned that the hard way.

i know the concept, i was questioning the scale - would it actually be a problem to lift a solid object instead of pumping water?

'cause i imagine it would be more efficient

obviously there's some problem or they would be doing it, but i'm interested in what the problem is

The trick with water is that (as you probably realise) it can be lifted bit by bit while an equivalent object of the same mass needs to be lifted in its entirety. So while it's a trivial problem to pump 10 tons of water through pipes 400 foot, moving 10 tons of steel is not a trivial problem as crane, lorry, and lift manufacturers will confirm. Moving 10,000 tons of water quickly starts to get into the non-trivial problem category while 10,000 tons of steel (in a way that's as useful for this purpose as water) is un-feasible.

ok, that makes sense - still, you could simply divide that huge solid object into n smaller objects, tho' that would introduce the problem of switching to the next one whenever one is lifted/lowered all the way

also, lifting 10 tons is a very trivial problem judging by a quick glance at some cranes http://www.bigge.com/crane-charts/ (some of those list over a kiloton)and obviously for our purposes, it wouldn't have to be mobile and would likely only need to work vertically, so that would make it even easier

I keep kicking that idea around in my head too, but i think the problem is that a system that can store a useful amount of power would be massive. I was surprised by how little power it takes to lift a really heavy weight quite a long way.

Try going the other way, imagine the largest system that could be built then calculate the amount of energy that could be stored in that way. Is it physically practical to move aloft a 30mx30mx30m block of iron 300m? You could build the system into a used quarry or something so you wouldnt have to build a giant building to support it. I have to go to a meeting so i dont have time to run the numbers, but im guessing that the amount of power stored isnt really that much. Still you could store it essentially forever.

but isn't the same true for water? only in an even bigger scale since water isn't particularly denseeither way you're going to need a lot of space, but i'm not convinced that's the bottleneck

i know the concept, i was questioning the scale - would it actually be a problem to lift a solid object instead of pumping water?

'cause i imagine it would be more efficient

obviously there's some problem or they would be doing it, but i'm interested in what the problem is

The trick with water is that (as you probably realise) it can be lifted bit by bit while an equivalent object of the same mass needs to be lifted in its entirety. So while it's a trivial problem to pump 10 tons of water through pipes 400 foot, moving 10 tons of steel is not a trivial problem as crane, lorry, and lift manufacturers will confirm. Moving 10,000 tons of water quickly starts to get into the non-trivial problem category while 10,000 tons of steel (in a way that's as useful for this purpose as water) is un-feasible.

ok, that makes sense - still, you could simply divide that huge solid object into n smaller objects, tho' that would introduce the problem of switching to the next one whenever one is lifted/lowered all the way

also, lifting 10 tons is a very trivial problem judging by a quick glance at some cranes http://www.bigge.com/crane-charts/ (some of those list over a kiloton)and obviously for our purposes, it wouldn't have to be mobile and would likely only need to work vertically, so that would make it even easier

I keep kicking that idea around in my head too, but i think the problem is that a system that can store a useful amount of power would be massive. I was surprised by how little power it takes to lift a really heavy weight quite a long way.

Try going the other way, imagine the largest system that could be built then calculate the amount of energy that could be stored in that way. Is it physically practical to move aloft a 30mx30mx30m block of iron 300m? You could build the system into a used quarry or something so you wouldnt have to build a giant building to support it. I have to go to a meeting so i dont have time to run the numbers, but im guessing that the amount of power stored isnt really that much. Still you could store it essentially forever.

but isn't the same true for water? only in an even bigger scale since water isn't particularly denseeither way you're going to need a lot of space, but i'm not convinced that's the bottleneck

Not really, water storage takes advantage of the terrain to form large reservoirs. Although you are right, water isnt that dense, water storage makes up for it by being massive in scale.

i know the concept, i was questioning the scale - would it actually be a problem to lift a solid object instead of pumping water?

'cause i imagine it would be more efficient

obviously there's some problem or they would be doing it, but i'm interested in what the problem is

The trick with water is that (as you probably realise) it can be lifted bit by bit while an equivalent object of the same mass needs to be lifted in its entirety. So while it's a trivial problem to pump 10 tons of water through pipes 400 foot, moving 10 tons of steel is not a trivial problem as crane, lorry, and lift manufacturers will confirm. Moving 10,000 tons of water quickly starts to get into the non-trivial problem category while 10,000 tons of steel (in a way that's as useful for this purpose as water) is un-feasible.

ok, that makes sense - still, you could simply divide that huge solid object into n smaller objects, tho' that would introduce the problem of switching to the next one whenever one is lifted/lowered all the way

also, lifting 10 tons is a very trivial problem judging by a quick glance at some cranes http://www.bigge.com/crane-charts/ (some of those list over a kiloton)and obviously for our purposes, it wouldn't have to be mobile and would likely only need to work vertically, so that would make it even easier

I keep kicking that idea around in my head too, but i think the problem is that a system that can store a useful amount of power would be massive. I was surprised by how little power it takes to lift a really heavy weight quite a long way.

Try going the other way, imagine the largest system that could be built then calculate the amount of energy that could be stored in that way. Is it physically practical to move aloft a 30mx30mx30m block of iron 300m? You could build the system into a used quarry or something so you wouldnt have to build a giant building to support it. I have to go to a meeting so i dont have time to run the numbers, but im guessing that the amount of power stored isnt really that much. Still you could store it essentially forever.

I think the biggest mistake being made in this solid vs water discussion is the assumption that we're storing huge amounts of energy in one place.

I mean, one person did the math on the entire wasted energy production of Texas wind farms for five years. I don't think anyone expects to store all the wasted wind energy from the second largest state in the nation for five years.

Why not break the problem down even smaller? Build a small tower next to each wind turbine, use electric power to lift a block of lead or some other relatively cheap buy very dense material, and drop it when you want the power back. Actually, you probably want a whole bunch of small blocks of lead in that one tower, so that you can spread out the gain over time. Unless there's a practical way to drop a really heavy block very slowly?

I never properly learned physics, but it seems like this would be possible. (EDIT: Just to clarify, I mean I don't know where to start with the math without a bit of google searching.)

I'm guessing the biggest difference between this type of system and water is that it probably requires more maintenance and might wear through parts quickly enough to offset its gains.

The biggest benefit is that it could be used in places where water is a scarce resource.

If you were really clever with the design, it could actually use the same generator as the wind turbine to generate the power, and as the motor to lift the block (or even use the wind power directly).

Also the failure mode of a water storage system is that the water leaks out to the lower lake. What about the failure mode of the 30m^3 block of iron? And what about when the price of electricity spikes mid transfer and you need to stop for a few hours.

The article and report presume that the energy storage need be chemical batteries. While that may be compact and convenient, there's really no reason that the excess energy could not be stored mechanically. There are lots of potential mechanical mechanisms to store energy: pumping water up hill, lifting heavy weights, compressing gases, heavy fly wheels, etc.

What ever happened to flywheels as a storage technology? I know a few years back, very large, spinning masses were supposed to be the bees-knees when it came to smoothing out demand spikes. Do they not hold enough energy to keep things going when the normal generation drops to zero or something?

Also the failure mode of a water storage system is that the water leaks out to the lower lake. What about the failure mode of the 30m^3 block of iron? And what about when the price of electricity spikes mid transfer and you need to stop for a few hours.

failure mode: drop the block to the ground via free fall

stopping: assuming our system is a weight on a pulley, secure the "rope" on the other end to the ground

Re: Solid vs liquid - I suppose you could use dry sand with a system to lift the sand to the top again. It should behave enough like a liquid to drive a turbine of sorts although you'd need to be careful of sand getting into the bearings.

re: Flywheels

Flywheels are great for smoothing out sudden spikes or troughs, however they do slow down so they need a constant injection of energy to keep spinning. I guess what they do with those is if there's a sudden drop in demand the excess energy is dumped into the flywheel and if there's a sudden spike in demand the power is drawn from the spinning flywheel. This means that the very expensive turbines that provide the main power generation can be changed granularly by raising or lowing the tempreture of the furnace or removing rods.

Also the failure mode of a water storage system is that the water leaks out to the lower lake. What about the failure mode of the 30m^3 block of iron? And what about when the price of electricity spikes mid transfer and you need to stop for a few hours.

I dont think ether of those are really significant issues. If the huge block of iron falls, it hits the ground. Just dont be underneath it when that happens and your fine. If you need to stop the transfer just stop lifting the weight, there is no reason you have to lift the weight all the way up.

A block weighing X kilograms lifted to a high of h meters will represent the stored energy in joules, which is also watt-seconds. 9.8 is the acceleration constant of gravity on earth.factor is the gravitational constant for earth.

Energy in joules = (weight kg)(9.8)(h meters)

Joules/3600 = watt-hours

Ok, lets test this out for a big system that would store a lot of power. For the math, we’ll select a big concrete block that weighs 10,000 kg, or roughly 11 Tons. We’ll lift it really high, say 10M, or about 33 feet. The lossless raw energy stored in this system would be:

Also the failure mode of a water storage system is that the water leaks out to the lower lake. What about the failure mode of the 30m^3 block of iron? And what about when the price of electricity spikes mid transfer and you need to stop for a few hours.

I dont think ether of those are really significant issues. If the huge block of iron falls, it hits the ground. Just dont be underneath it when that happens and your fine. If you need to stop the transfer just stop lifting the weight, there is no reason you have to lift the weight all the way up.

That's really all there is to it? A block massive enough to hold grid-relevant amounts of gravitational energy hits the ground in one giant "thump" and everything's fine so long as you're not directly underneath it?

How about the EROI (remember the thing the entire article was about?) for a massive system of cranks, pulleys and supports for this Wiley E. Coyote contraption?

Also the failure mode of a water storage system is that the water leaks out to the lower lake. What about the failure mode of the 30m^3 block of iron? And what about when the price of electricity spikes mid transfer and you need to stop for a few hours.

I dont think ether of those are really significant issues. If the huge block of iron falls, it hits the ground. Just dont be underneath it when that happens and your fine. If you need to stop the transfer just stop lifting the weight, there is no reason you have to lift the weight all the way up.

That's really all there is to it? A block massive enough to hold grid-relevant amounts of gravitational energy hits the ground in one giant "thump" and everything's fine so long as you're not directly underneath it?

How about the EROI (remember the thing the entire article was about?) for a massive system of cranks, pulleys and supports for this Wiley E. Coyote contraption?

And all this just because water isn't dense enough?

Yea, as i said at the outset, the problem is that the thing has to be prohibitively massive to store any amount of power.

Werent you the one who was complaining about "Follow up response revealing complete obliviousness to why bad things about bad idea are bad" Maybe you should try actually reading the comments instead of blaterhing on about how everyone else is making a "whooshing sound".

A block weighing X kilograms lifted to a high of h meters will represent the stored energy in joules, which is also watt-seconds. 9.8 is the acceleration constant of gravity on earth.factor is the gravitational constant for earth.

Energy in joules = (weight kg)(9.8)(h meters)

Joules/3600 = watt-hours

Ok, lets test this out for a big system that would store a lot of power. For the math, we’ll select a big concrete block that weighs 10,000 kg, or roughly 11 Tons. We’ll lift it really high, say 10M, or about 33 feet. The lossless raw energy stored in this system would be:

A block weighing X kilograms lifted to a high of h meters will represent the stored energy in joules, which is also watt-seconds. 9.8 is the acceleration constant of gravity on earth.factor is the gravitational constant for earth.

Energy in joules = (weight kg)(9.8)(h meters)

Joules/3600 = watt-hours

Ok, lets test this out for a big system that would store a lot of power. For the math, we’ll select a big concrete block that weighs 10,000 kg, or roughly 11 Tons. We’ll lift it really high, say 10M, or about 33 feet. The lossless raw energy stored in this system would be:

Indeed, and the last thing we need is to pair a sometimes dangerous battery technology (lithium based) with a dangerous power source (wind power generation has killed more than 30 people this year so far)And you know, little things like fires (if there's a problem with the brake used when the wind is high, they tend to catch fire) also don't go well with lithium batteries.

How did 30 people die? I'd be very interested in reading more about this.

And we should never use any energy source which was dangerous in any way right?

Quote:

Death Rate (deaths per TWh)100.____Coal (elect, heat,cook –world avg) (26% of world energy, 50% of electricity)_36.____Oil (36% of world energy)__4.____Natural Gas (21% of world energy)__0.44__Solar (rooftop) (0.2% of world energy for all solar)__0.15__Wind (1.6% of world energy)__0.04__Nuclear (5.9% of world energy)

I work in this industry and have seen some of the numbers and problems that come across in this topic.

To many it is indeed surprising that we "shed" excess energy through mechanisms like transforming it to heat and releasing it.

There are a number of reasons, and perhaps the simplest is simply that storage of large scale energy is very immature at this point.

In order for shedding to be a "worse" solution than storing, the "cost lost" by shedding PLUS the "cost to generate" when needed again would have to be more than the "cost saved" by not reproducing the energy when it's needed. That "cost gained" would come ideally from some asset that is bought at a fixed price and maintained at a low cost, plus can be immediately accessible as load changes.

But the truth is that none exist. It is simply too expensive right now to save energy. Trust me, the energy sector is very interested in cost efficient storage, but it doesn't exist.

Scale is definitely a part of the problem. We don't have to store the energy someone needs to run their car. Such "spikes" are non-issues on the generating line.

I'll explain why such changes are insignificant.

To generate electricity, a generator is spinning somewhere. This generator is huge. It has more coils on it than I really know about, but I can say it's a lot. It has to spin at the same rate as the rest of the entire United States (except Texas because ... Texas) and with the exact same timing because the entire US electric grid is interconnected and electricity can even be shared among them. Even without sharing though, that one generator is generating so much power than a single company could probably turn their entire building off and on continually and the difference in spin necessary to meet the changed load is so small it is accommodated mechanically in near-real-time.

However, sometimes things happen where load changes fast. The number one rule is that the generator must spin with the same timing as the rest of the grid. So if your load changes a lot, that generator's output is either too much or not enough and the generator will try to change its rate of spin. THIS CANNOT BE ALLOWED!

So an immediate response outside the generator is needed.

Right now, if that means the generator would slow down (because load just dropped) artificial load is created and shed. That is load like heat shedding.

If more load is needed, then a new generator is added to the grid. And by the way, depending on the size of that generator, it might have been running in 100% "shedding" mode for days because the largest generators need that kind of time to speed up and then synch to the grid. Smaller ones require less time.

Ideally, if you're generating too much load, you can sell it to someone across the US. That is why the US is a grid that is country wide and such deals do get brokered, but they're brokered based on forecast load. Never as a result of emergency load.

Emergency load does sometimes get moved in this way though, at substantial contract costs.

All of this precise timing and load sharing could ideally go away with some sort of storage. But right now, that storage isn't practical.

Here are the commonly available storage options:

Batteries. Not practical at the massive load levels of the transmission network. Imagine the size of battery you need to generate 12 volts reliably for your car. Now consider that transmission lines are rated sometimes up to multiple thousand megawatts. The size of the potential battery is huge, even with the latest trends in batteries (like the ones used in cell phones). Plus it would be a potential waste nightmare as much of the contents of some types of batteries are hazardous.

Water. It is possible to construct towers that pump water when you have excess load and then allow gravity to "unpump" the water when you need it - thus turning a turbine at that time. However, the cost to pump the water against gravity is very inefficient due to the efficiency levels of hydro pumps.

Saline solutions. It's possible to convert heat in to saline solutions that can store it for very long periods of time then extract the heat as electricity when you need it. This is the most promising of cost that I've ever seen and yet it's still much much worse than just generating more as demand needs it or shedding some when demand doesn't.

Instead, mitigation plans for "shed now" mean basically "get rid of it as fast as you can" - such as with heat dissipation, or maybe ideally, selling it remotely.

Mitigation for "we need more now" involve spinning up generators of various sizes and putting them on the grid as you need them. These generators cost more the less they produce (in terms of cost per MW and in terms of maintenance costs) yet still are much much cheaper than any storage solution.

And that's why it happens.

In other words, the grid usually is the most efficient way to store and redistribute energy - exactly what it was designed to do.

The problems associated with shedding power are mostly political and economic. The generators that shed are unable to sell all of their capacity, while those that remain online continue to profit (wind vs dams, for example).

Also the failure mode of a water storage system is that the water leaks out to the lower lake.

Taum Sauk

I note in that example the failure mode was that it leaked. They then lined it but failed to check that the leaking hadn't caused any damage to the surrounds that needed to be fixed. Subsequently they then overfilled it leading to catastrophic failure.

So yes, the final failure (after everything went wrong repeatedly due to mismangement) was devestating to the surrounding country side, however if one of the pumps, turbines, or gates had failed then the water would have either leaked back down, or never made it up in the first place. And what does it take to repair those items, how much do you have to dismantle to do so?

With the suspended weight, what happens if a cable pops off a pulley or snaps?

Indeed, and the last thing we need is to pair a sometimes dangerous battery technology (lithium based) with a dangerous power source (wind power generation has killed more than 30 people this year so far)And you know, little things like fires (if there's a problem with the brake used when the wind is high, they tend to catch fire) also don't go well with lithium batteries.

How did 30 people die? I'd be very interested in reading more about this.

It sounds like a prefab talking point; but the occupational safety record of industries that involve 'climbing tall objects while the boss breathes down your neck about climbing them faster' isn't all that hot, and the turbines that aren't little hobby projects can be pretty tall indeed. Hazards probably double if anybody has put in nontrivial quantities of offshore capacity: flying a helicopter near a bunch of giant turbines probably isn't wise; but docking on a pole sticking out of the open water, with wave action, is also no picnic.

I don't know if 30 is actually the number; but what we'd really want to know is how it stacks up in terms of kills per unit capacity. We know that coal (mining and burning) chews people up, same with oil, gas burns fairly clean; but isn't exactly a pleasure to extract; people die just keeping branches away from power lines, if their luck runs out and they aren't clipped in properly.

For most human activity, the question isn't "does it kill people?"; but "how does it compare to the alternatives?"; because it almost all kills people.